Quasi-harmonic approaches provide an economical route to modeling the temperature dependence of molecular crystal structures and properties. Several studies have demonstrated good performance of these models, at least for rigid molecules, when using fragment-based approaches with correlated wavefunction techniques. Many others have found success employing dispersion-corrected density functional theory (DFT). Here, a hierarchy of models in which the energies, geometries, and phonons are computed either with correlated methods or DFT are examined to identify which combinations produce useful predictions for properties such as the molar volume, enthalpy, and entropy as a function of temperature. The results demonstrate that refining DFT geometries and phonons with single-point energies based on dispersion-corrected second-order Møller–Plesset perturbation theory can provide clear improvements in the molar volumes and enthalpies compared to those obtained from DFT alone. Predicted entropies, which are governed by vibrational contributions, benefit less clearly from the hybrid schemes. Using these hybrid techniques, the room-temperature thermochemistry of acetaminophen (paracetamol) is predicted to address the discrepancy between two experimental sublimation enthalpy measurements.

中文翻译：

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识别用于模拟分子晶体热膨胀的实用准谐波电子结构方法

准谐波方法为建模分子晶体结构和性质的温度依赖性提供了一种经济的途径。几项研究表明，当使用基于片段的方法和相关波函数技术时，至少对于刚性分子而言，这些模型具有良好的性能。使用分散校正的密度泛函理论（DFT），其他许多人也获得了成功。在这里，检查了模型的层次结构，其中使用相关方法或DFT计算了能量，几何形状和声子，以确定哪些组合对诸如摩尔体积，焓和熵随温度的变化等性质产生了有用的预测。结果表明，与仅从DFT获得的摩尔体积和焓相比，基于色散校正的二阶Møller-Plesset微扰理论，利用单点能量细化DFT几何形状和声子可以明显改善摩尔体积和焓。由振动贡献控制的预测熵从混合方案中受益较少。使用这些混合技术，可以预测对乙酰氨基酚（对乙酰氨基酚）的室温热化学可解决两次实验升华焓测量之间的差异。